– Pope Leo this week repudiated a major teaching used by the Catholic Church since at ​least the fifth century to evaluate when countries might be justified in waging wars, in a move experts said could have long-reaching impact ‌for global powers.

The disavowal of the doctrine came in the pope’s first major document, issued on Monday, which also urged global regulation of AI systems and made the clearest apology yet for the Catholic Church’s historic role in supporting transatlantic slavery.”The ‘just war’ theory which has all too often been used to justify any kind of war, is now outdated,” wrote Leo in the encyclical, entitled “Magnifica Humanitas” (Magnificent Humanity).

“Humanity possesses ​far more effective and capable tools for promoting human life and resolving conflicts, such as dialogue, diplomacy and forgiveness,” he said.Chicago Cardinal Blase Cupich, a ​close ally of Leo who was at the Vatican for the presentation of the text on Monday, told Reuters the pope is ⁠concerned with how the theory has been used by world leaders to justify going to war.
“We have to make clear that the just war theory was always ​meant to be a restraint, not a permission slip which sadly some are misusing to justify their decisions to go to war rather than seek the ways of peace,” ​said Cupich.

Leo, who has adopted a more forceful tone in recent months and has drawn the ire of U.S. President Donald Trump after criticising the Iran war, decried the number of wars roiling the world in his text and warned that arms industry profits were a driving force behind conflicts.